In a second fatwā in 1998, bin Laden outlined his objections to American foreign policy with respect to Israel, as well as the continued presence of American troops in Saudi Arabia after the Gulf War.[9] Bin Laden used Islamic texts to exhort Muslims to attack Americans until the stated grievances are reversed. Muslim legal scholars "have throughout Islamic history unanimously agreed that the jihad is an individual duty if the enemy destroys the Muslim countries.", according to bin Laden.[9]

Osama bin Laden

Bin Laden, who orchestrated the attacks, initially denied but later admitted involvement.[1][10][11]Al Jazeera broadcast a statement by bin Laden on September 16, 2001, stating, "I stress that I have not carried out this act, which appears to have been carried out by individuals with their own motivation."[12] In November 2001, U.S. forces recovered a videotape from a destroyed house in Jalalabad, Afghanistan. In the video, bin Laden is seen talking to Khaled al-Harbi and admits foreknowledge of the attacks.[13] On December 27, 2001, a second bin Laden video was released. In the video, he said, "It has become clear that the West in general and America in particular have an unspeakable hatred for Islam....It is the hatred of crusaders. Terrorism against America deserves to be praised because it was a response to injustice, aimed at forcing America to stop its support for Israel, which kills our people...We say that the end of the United States is imminent, whether Bin Laden or his followers are alive or dead, for the awakening of the Muslim umma (nation) has occurred", but he stopped short of admitting responsibility for the attacks.[14] The transcript references several times to the United States specifically targeting Muslims.

Shortly before the U.S. presidential election in 2004, in a taped statement, bin Laden publicly acknowledged al-Qaeda's involvement in the attacks on the U.S. and admitted his direct link to the attacks. He said that the attacks were carried out because, "we are free ... and want to regain freedom for our nation. As you undermine our security we undermine yours."[15] Bin Laden said he had personally directed his followers to attack the World Trade Center.[11][16] Another video obtained by Al Jazeera in September 2006 shows bin Laden with Ramzi bin al-Shibh, as well as two hijackers, Hamza al-Ghamdi and Wail al-Shehri, as they make preparations for the attacks.[17] The U.S. never formally indicted bin Laden for the 9/11 attacks but he was on the FBI's Most Wanted List for the bombings of the U.S. Embassies in Dar es Salaam, Tanzania, and Nairobi, Kenya.[18][19] After a 10-year manhunt, bin Laden was killed by American special forces in a compound in Abbottabad, Pakistan on May 2, 2011.[20][21]

Khalid Sheikh Mohammed

The journalist Yosri Fouda of the Arabic television channel Al Jazeera reported that, in April 2002, Khalid Sheikh Mohammed admitted his involvement, along with Ramzi bin al-Shibh.[22][23][24] The 9/11 Commission Report determined that the animosity towards the United States felt by Mohammed, the principal architect of the 9/11 attacks, stemmed from his "violent disagreement with U.S. foreign policy favoring Israel".[25] Mohammed was also an adviser and financier of the 1993 World Trade Center bombing and the uncle of Ramzi Yousef, the lead bomber in that attack.[26][27]

Mohammed was arrested on March 1, 2003, in Rawalpindi, Pakistan, by Pakistani security officials working with the CIA, then transported to Guantanamo Bay and interrogated using methods including waterboarding.[28][29] During U.S. hearings at Guantanamo Bay in March 2007, Mohammed again confessed his responsibility for the attacks, stating he "was responsible for the 9/11 operation from A to Z" and that his statement was not made under duress.[24][30]

Other al-Qaeda members

In "Substitution for Testimony of Khalid Sheikh Mohammed" from the trial of Zacarias Moussaoui, five people are identified as having been completely aware of the operation's details. They are bin Laden, Khalid Sheikh Mohammed, Ramzi bin al-Shibh, Abu Turab al-Urduni, and Mohammed Atef.[31] To date, only peripheral figures have been tried or convicted for the attacks.

On September 26, 2005, the Spanish high court sentenced Abu Dahdah to 27 years in prison for conspiracy on the 9/11 attacks and being a member of the terrorist organization al-Qaeda. At the same time, another 17 al-Qaeda members were sentenced to penalties of between six and eleven years.[32] On February 16, 2006, the Spanish Supreme Court reduced the Abu Dahdah penalty to 12 years because it considered that his participation in the conspiracy was not proven.[33]

Also, in 2006, Moussaoui, who some originally suspected might have been the assigned 20th hijacker, was convicted for the lesser role of conspiracy to commit acts of terrorism and air piracy. He is serving a life sentence without parole in the United States.[34][35]Mounir el-Motassadeq, an associate of the Hamburg-based hijackers, is serving 15 years in Germany for his role in helping the hijackers prepare for the attacks.[36]

Motives

Osama bin Laden's declaration of a holy war against the United States, and a 1998 fatwā signed by bin Laden and others, calling for the killing of Americans,[9] are seen by investigators as evidence of his motivation.[39] In bin Laden's November 2002 "Letter to America", he explicitly stated that al-Qaeda's motives for their attacks include

After the attacks, bin Laden and al-Zawahiri released additional video tapes and audio tapes, some of which repeated those reasons for the attacks. Two particularly important publications were bin Laden's 2002 "Letter to America",[45] and a 2004 video tape by bin Laden.[46]

Bin Laden interpreted Muhammad as having banned the "permanent presence of infidels in Arabia".[47] In 1996, bin Laden issued a fatwā calling for American troops to leave Saudi Arabia. In 1998, al-Qaeda wrote, "for over seven years the United States has been occupying the lands of Islam in the holiest of places, the Arabian Peninsula, plundering its riches, dictating to its rulers, humiliating its people, terrorizing its neighbors, and turning its bases in the Peninsula into a spearhead through which to fight the neighboring Muslim peoples."[48]

In a December 1999 interview, bin Laden said he felt that Americans were "too near to Mecca", and considered this a provocation to the entire Muslim world.[49] One analysis of suicide terrorism suggested that without U.S. troops in Saudi Arabia, al-Qaeda likely would not have been able to get people to commit to suicide missions.[50]

In the 1998 fatwā, al-Qaeda identified the Iraq sanctions as a reason to kill Americans, condemning the "protracted blockade"[48] among other actions that constitute a declaration of war against "Allah, his messenger, and Muslims."[48] The fatwā declared that "the ruling to kill the Americans and their allies – civilians and military – is an individual duty for every Muslim who can do it in any country in which it is possible to do it, in order to liberate the al-Aqsa Mosque and the holy mosque of Mecca from their grip, and in order for their [the Americans'] armies to move out of all the lands of Islam, defeated and unable to threaten any Muslim."[9][51]

Bin Laden claimed, in 2004, that the idea of destroying the towers had first occurred to him in 1982, when he witnessed Israel's bombardment of high-rise apartment buildings during the 1982 Lebanon War.[52][53] Some analysts, including Mearsheimer and Walt, also claim that one motivation for the attacks was U.S. support of Israel.[41][49] In 2004 and 2010, bin Laden again connected the September 11 attacks with U.S. support of Israel, although most of the letter expressed bin Laden's disdain for President Bush and bin Laden's hope to "destroy and bankrupt" the U.S.[54][55]

Other motives have been suggested in addition to those stated by bin Laden and al-Qaeda, including western support of Islamic and non-Islamic authoritarian regimes in Saudi Arabia, Iran, Egypt, Iraq, Pakistan and northern Africa, and the presence of western troops in some of these countries.[56] Some authors suggest the "humiliation" resulting from the Islamic world falling behind the Western world – this discrepancy rendered especially visible by the globalization trend[57][58] and a desire to provoke the U.S. into a broader war against the Islamic world in the hope of motivating more allies to support al-Qaeda. Similarly, others have argued that 9/11 was a strategic move with the objective of provoking America into a war that would incite a pan-Islamic revolution.[59][60]

In late 1998 or early 1999, bin Laden gave approval for Mohammed to go forward with organizing the plot. A series of meetings occurred in early 1999, involving Mohammed, bin Laden, and his deputy Mohammed Atef.[62] Atef provided operational support for the plot, including target selections and helping arrange travel for the hijackers.[62] Bin Laden overruled Mohammed, rejecting some potential targets such as the U.S. Bank Tower in Los Angeles because, "there was not enough time to prepare for such an operation".[63][64]

Diagram showing the attacks on the World Trade Center

Bin Laden provided leadership and financial support for the plot, and was involved in selecting participants.[65] Bin Laden initially selected Nawaf al-Hazmi and Khalid al-Mihdhar, both experienced jihadists who had fought in Bosnia. Hazmi and Mihdhar arrived in the United States in mid-January 2000. In spring 2000, Hazmi and Mihdhar took flying lessons in San Diego, California, but both spoke little English, performed poorly with flying lessons, and eventually served as secondary – or "muscle" – hijackers.[66][67]

In late 1999, a group of men from Hamburg, Germany arrived in Afghanistan, including Mohamed Atta, Marwan al-Shehhi, Ziad Jarrah, and Ramzi bin al-Shibh.[68] Bin Laden selected these men because they were educated, could speak English, and had experience living in the West.[69] New recruits were routinely screened for special skills and al-Qaeda leaders consequently discovered that Hani Hanjour already had a commercial pilot's license.[70]

Hanjour arrived in San Diego on December 8, 2000, joining Hazmi.[71]:6-7 They soon left for Arizona, where Hanjour took refresher training.[71]:7 Marwan al-Shehhi arrived at the end of May 2000, while Atta arrived on June 3, 2000, and Jarrah arrived on June 27, 2000.[71]:6 Bin al-Shibh applied several times for a visa to the United States, but as a Yemeni, he was rejected out of concerns he would overstay his visa and remain as an illegal immigrant.[71]:4, 14 Bin al-Shibh stayed in Hamburg, providing coordination between Atta and Mohammed.[71]:16 The three Hamburg cell members all took pilot training in South Florida.[71]:6

In spring 2001, the secondary hijackers began arriving in the United States.[72] In July 2001, Atta met with bin al-Shibh in Spain, where they coordinated details of the plot, including final target selection. Bin al-Shibh also passed along bin Laden's wish for the attacks to be carried out as soon as possible.[73]

American Airlines Flight 11: a Boeing 767 aircraft, departed Boston's Logan Airport at 7:59 a.m. en route to Los Angeles with a crew of 11 and 76 passengers, not including five hijackers. The hijackers flew the plane into the North Tower of the World Trade Center at 8:46 a.m.

United Airlines Flight 175: a Boeing 767 aircraft, departed Logan Airport at 8:14 a.m. en route to Los Angeles with a crew of nine and 51 passengers, not including five hijackers. The hijackers flew the plane into the South Tower of the World Trade Center at 9:03 a.m.

A fourth flight, United Airlines Flight 93, under the control of four hijackers, crashed near Shanksville, Pennsylvania, southeast of Pittsburgh, at 10:03 a.m. after the passengers fought the hijackers. Flight 93's target is believed to have been either the Capitol or the White House.[75] Flight 93's cockpit voice recorder revealed crew and passengers tried to seize control of the plane from the hijackers after learning through phone calls that Flights 11, 77, and 175 had been crashed into buildings that morning.[81] Once it became evident to the hijackers that the passengers might regain control of the plane, the hijackers rolled the plane and intentionally crashed it.[82][83]

The north face of Two World Trade Center (south tower) immediately after being struck by United Airlines Flight 175

Some passengers and crew members who called from the aircraft using the cabin airphone service and mobile phones provided details: several hijackers were aboard each plane; they used mace, tear gas, or pepper spray to overcome attendants; and some people aboard had been stabbed.[84][85][86][87][88][89][90] Reports indicated hijackers stabbed and killed pilots, flight attendants, and one or more passengers.[74][91] In their final report, the 9/11 Commission found the hijackers had recently purchased multi-function hand tools and assorted knives and blades.[92][93] A flight attendant on Flight 11, a passenger on Flight 175, and passengers on Flight 93 said the hijackers had bombs, but one of the passengers said he thought the bombs were fake. The FBI found no traces of explosives at the crash sites, and the 9/11 Commission concluded that the bombs were probably fake.[74]

Three buildings in the World Trade Center complex collapsed due to fire-induced structural failure.[94] The South Tower collapsed at 9:59 a.m. after burning for 56 minutes in a fire caused by the impact of United Airlines Flight 175 and the explosion of its fuel.[94] The North Tower collapsed at 10:28 a.m. after burning for 102 minutes.[94] When the North Tower collapsed, debris fell on the nearby 7 World Trade Center building (7 WTC), damaging it and starting fires. These fires burned for hours, compromising the building's structural integrity, and 7 WTC collapsed at 5:21 p.m.[95][96] The west side of the Pentagon sustained significant damage.

Security camera footage of Flight 77 hitting the Pentagon.[97] The plane hits the Pentagon approximately 86 seconds after the beginning of this recording.

At 9:42 a.m., the Federal Aviation Administration (FAA) grounded all aircraft within the continental U.S., and aircraft already in flight were told to land immediately.[98] All international civilian aircraft were either turned back or redirected to airports in Canada or Mexico, and all international flights were banned from landing on United States territory for three days.[99] The attacks created widespread confusion among news organizations and air traffic controllers. Among the unconfirmed and often contradictory news reports aired throughout the day, one of the most prevalent said a car bomb had been detonated at the U.S. State Department's headquarters in Washington, D.C.[100] Another jet—Delta Air Lines Flight 1989—was suspected of having been hijacked, but the aircraft responded to controllers and landed safely in Cleveland, Ohio.[101]

In a April 2002 interview, Khalid Sheikh Mohammed and Ramzi bin al-Shibh, who are believed to have organized the attacks, said Flight 93's intended target was the United States Capitol, not the White House.[102] During the planning stage of the attacks, Mohamed Atta, the hijacker and pilot of Flight 11, thought the White House might be too tough a target and sought an assessment from Hani Hanjour, who would later hijack and pilot Flight 77.[103] Mohammed said al-Qaeda initially planned to target nuclear installations rather than the World Trade Center and the Pentagon, but decided against it, fearing things could "get out of control".[104] Final decisions on targets, according to Mohammed, were left in the hands of the pilots.[103]

Casualties

The attacks resulted in the deaths of 2,996 people, including the 19 hijackers.[105] The 2,977 victims included 246 on the four planes (from which there were no survivors), 2,606 in the World Trade Center and in the surrounding area, and 125 at the Pentagon.[106][107] Nearly all of those who perished were civilians with the exceptions of 72 law enforcement officers, 343 firefighters, and 55 military personnel who died in the attacks.[108][109] After New York, New Jersey lost the most state citizens, with the city of Hoboken having the most citizens that died in the attacks.[110] More than 90 countries lost citizens in the September 11 attacks.[111] The attacks of September 11, 2001, marked it the worst terrorist attack in world history and the deadliest foreign act of destruction to life and property on American soil since the Japanese surprise attack on Pearl Harbor on December 7, 1941.[3][not in citation given]

In Arlington County, 125 Pentagon workers lost their lives when Flight 77 crashed into the western side of the building. Of these, 70 were civilians and 55 were military personnel, many of them who worked for the United States Army or the United States Navy. The Army lost 47 civilian employees, six civilian contractors, and 22 soldiers, while the Navy lost six civilian employees, three civilian contractors, and 33 sailors. Seven Defense Intelligence Agency (DIA) civilian employees were also among the dead in the attack, as well as an Office of the Secretary of Defense (OSD) contractor.[112][113][114]Lieutenant GeneralTimothy Maude, an Army Deputy Chief of Staff, was the highest-ranking military official killed at the Pentagon.[115]

Burning towers with view from Statue of Liberty

In New York City, more than 90% of the workers and visitors who died in the towers had been at or above the points of impact.[116] In the North Tower, 1,355 people at or above the point of impact were trapped and died of smoke inhalation, fell or jumped from the tower to escape the smoke and flames, or were killed in the building's eventual collapse. The destruction of all three staircases in the tower when Flight 11 hit made it impossible for anyone above the impact zone to escape. 107 people below the point of impact died as well.[116]

In the South Tower, one stairwell, Stairwell A, was left intact after Flight 175 hit, allowing 14 people located on the floors of impact (including one man who saw the plane coming at him) and four more from the floors above to escape. 911 operators who received calls from individuals inside the tower were not well informed of the situation as it rapidly unfolded and as a result, told callers not to descend the tower on their own.[117] 630 people died in that tower, fewer than half the number killed in the North Tower.[116] Casualties in the South Tower were significantly reduced by some occupants deciding to start evacuating as soon as the North Tower was struck.[118]

Urban Search and Rescue Task Force German Shepherd dog works to uncover survivors at the site of the collapsed World Trade Center after the September 11, 2001 attacks.

At least 200 people fell or jumped to their deaths from the burning towers (as exemplified in the photograph The Falling Man), landing on the streets and rooftops of adjacent buildings hundreds of feet below.[119] Some occupants of each tower above the point of impact made their way toward the roof in hope of helicopter rescue, but the roof access doors were locked. No plan existed for helicopter rescues, and the combination of roof equipment and thick smoke and intense heat prevented helicopters from approaching.[120] A total of 414 emergency workers died as they tried to rescue people and fight fires. The New York City Fire Department (FDNY) lost 341 firefighters and two paramedics.[121] The New York City Police Department (NYPD) lost 23 officers.[122] The Port Authority Police Department (PAPD) lost 37 officers.[123] Three New York State Court Officers were killed.[124] Eight emergency medical technicians (EMTs) and paramedics from private emergency medical services units were killed.[125][126]

Cantor Fitzgerald L.P., an investment bank on the 101st–105th floors of the North Tower, lost 658 employees, considerably more than any other employer.[127]Marsh Inc., located immediately below Cantor Fitzgerald on floors 93–100, lost 358 employees,[128][129] and 175 employees of Aon Corporation were also killed.[130] The National Institute of Standards and Technology (NIST) estimated that about 17,400 civilians were in the World Trade Center complex at the time of the attacks. Turnstile counts from the Port Authority suggest 14,154 people were typically in the Twin Towers by 8:45 a.m.[131][132] The vast majority of people below the impact zone safely evacuated the buildings.[133]

Weeks after the attack, the death toll was estimated to be over 6,000, more than twice the number of deaths eventually confirmed.[140] The city was only able to identify remains for about 1,600 of the World Trade Center victims. The medical examiner's office collected "about 10,000 unidentified bone and tissue fragments that cannot be matched to the list of the dead".[141] Bone fragments were still being found in 2006 by workers who were preparing to demolish the damaged Deutsche Bank Building. In 2010, a team of anthropologists and archaeologists searched for human remains and personal items at the Fresh Kills Landfill, where seventy-two more human remains were recovered, bringing the total found to 1,845. DNA profiling continues in an attempt to identify additional victims.[142][143][144] The remains are being held in storage in Memorial Park, outside the New York City Medical Examiner’s facilities. It was expected that the remains would be moved in 2013 to a repository behind a wall at the 9/11 museum. In July 2011, a team of scientists at the Office of Chief Medical Examiner was still trying to identify remains, in the hope that improved technology will allow them to identify other victims.[144] On March 20, 2015, the 1,640th victim was identified. There are still 1,113 victims who have not been identified.[145]

The Pentagon was severely damaged by the impact of American Airlines Flight 77 and ensuing fires, causing one section of the building to collapse.[155] As the airplane approached the Pentagon, its wings knocked down light poles and its right engine hit a power generator before crashing into the western side of the building.[156][157] The plane hit the Pentagon at the first-floor level. The front part of the fuselage disintegrated on impact, while the mid and tail sections kept moving for another fraction of a second.[158] Debris from the tail section penetrated furthest into the building, breaking through 310 feet (94 m) of the three outermost of the building's five rings.[158][159]

Rescue efforts

The New York City Fire Department deployed 200 units (half of the department) to the World Trade Center. Their efforts were supplemented by numerous off-duty firefighters and emergency medical technicians.[160][161][162] The New York City Police Department sent Emergency Service Units and other police personnel, and deployed its aviation unit. Once on the scene, the FDNY, NYPD, and PAPD did not coordinate efforts and performed redundant searches for civilians.[160][163] As conditions deteriorated, the NYPD aviation unit relayed information to police commanders, who issued orders for its personnel to evacuate the towers; most NYPD officers were able to safely evacuate before the buildings collapsed.[163][164] With separate command posts set up and incompatible radio communications between the agencies, warnings were not passed along to FDNY commanders.

After the first tower collapsed, FDNY commanders issued evacuation warnings; however, due to technical difficulties with malfunctioning radio repeater systems, many firefighters never heard the evacuation orders. 9-1-1 dispatchers also received information from callers that was not passed along to commanders on the scene.[161] Within hours of the attack, a substantial search and rescue operation was launched. After months of around-the-clock operations, the World Trade Center site was cleared by the end of May 2002.[165]

Eight hours after the attacks, Donald Rumsfeld, then U.S. Secretary of Defense, declares "The Pentagon is functioning."

At 8:32 a.m., FAA officials were notified Flight 11 had been hijacked and they in turn notified the North American Aerospace Defense Command (NORAD). NORAD scrambled two F-15s from Otis Air National Guard Base in Massachusetts and they were airborne by 8:53 a.m.[166] Because of slow and confused communication from FAA officials, NORAD had 9 minutes' notice that Flight 11 had been hijacked, and no notice about any of the other flights before they crashed.[166] After both of the Twin Towers had already been hit, more fighters were scrambled from Langley Air Force Base in Virginia at 9:30 a.m.[166] At 10:20 a.m. Vice President Dick Cheney issued orders to shoot down any commercial aircraft that could be positively identified as being hijacked. However, these instructions were not relayed in time for the fighters to take action.[166][167][168][169] Some fighters took to the air without live ammunition, knowing that to prevent the hijackers from striking their intended targets, the pilots might have to intercept and crash their fighters into the hijacked planes, possibly ejecting at the last moment.[170]

For the first time in U.S. history, SCATANA was invoked,[171] thus stranding tens of thousands of passengers across the world.[172] The FAA closed American airspace to all international flights, causing about five hundred flights to be turned back or redirected to other countries. Canada received 226 of the diverted flights and launched Operation Yellow Ribbon to deal with the large numbers of grounded planes and stranded passengers.[173]

The 9/11 attacks had immediate effects upon the American people.[174] Police and rescue workers from around the country took leaves of absence, traveling to New York City to help recover bodies from the twisted remnants of the Twin Towers.[175] Blood donations across the U.S. surged in the weeks after 9/11.[176][177]

The deaths of adults in the attacks resulted in over 3,000 children losing a parent.[178] Subsequent studies documented children's reactions to these actual losses and to feared losses of life, the protective environment in the aftermath of the attacks, and effects on surviving caregivers.[179][180][181]

Domestic reactions

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At a joint session of Congress, President Bush pledges to defend America's freedom against the fear of terrorism, September 20, 2001 (audio only).

Following the attacks, President Bush's approval rating soared to 90%.[182] On September 20, 2001, he addressed the nation and a joint session of the United States Congress regarding the events of September 11 and the subsequent nine days of rescue and recovery efforts, and described his intended response to the attacks. New York City mayor Rudy Giuliani's highly visible role won him high praise in New York and nationally.[183]

Many relief funds were immediately set up to assist victims of the attacks, with the task of providing financial assistance to the survivors of the attacks and to the families of victims. By the deadline for victim's compensation on September 11, 2003, 2,833 applications had been received from the families of those who were killed.[184]

Contingency plans for the continuity of government and the evacuation of leaders were implemented soon after the attacks.[172] However, Congress was not told that the United States had been under a continuity of government status until February 2002.[185]

In the largest restructuring of the U.S. government in contemporary history, the United States enacted the Homeland Security Act of 2002, creating the Department of Homeland Security. Congress also passed the USA PATRIOT Act, saying it would help detect and prosecute terrorism and other crimes.[186] Civil liberties groups have criticized the PATRIOT Act, saying it allows law enforcement to invade the privacy of citizens and that it eliminates judicial oversight of law enforcement and domestic intelligence.[187][188][189] In an effort to effectively combat future acts of terrorism, the National Security Agency (NSA) was given broad powers. NSA commenced warrantless surveillance of telecommunications, which was sometimes criticized since it permitted the agency "to eavesdrop on telephone and e-mail communications between the United States and people overseas without a warrant".[190] In response to requests by various intelligence agencies, the United States Foreign Intelligence Surveillance Court permitted an expansion of powers by the U.S. government in seeking, obtaining, and sharing information on U.S. citizens as well as non-U.S. people from around the world.[191]

Hate crimes

A fireman looks up at the remains of the South Tower

A fireman stands behind rubble

Shortly after the attacks, President Bush made a public appearance at Washington's largest Islamic Center and acknowledged the "incredibly valuable contribution" that millions of American Muslims made to their country and called for them "to be treated with respect."[192] However, numerous incidents of harassment and hate crimes against Muslims and South Asians were reported in the days following the attacks.[193][194][195]Sikhs were also targeted because Sikh males usually wear turbans, which are stereotypically associated with Muslims. There were reports of attacks on mosques and other religious buildings (including the firebombing of a Hindu temple), and assaults on people, including one murder: Balbir Singh Sodhi, a Sikh mistaken for a Muslim, was fatally shot on September 15, 2001, in Mesa, Arizona.[195]

According to an academic study, people perceived to be Middle Eastern were as likely to be victims of hate crimes as followers of Islam during this time. The study also found a similar increase in hate crimes against people who may have been perceived as Muslims, Arabs, and others thought to be of Middle Eastern origin.[196] A report by the South Asian American advocacy group known as South Asian Americans Leading Together, documented media coverage of 645 bias incidents against Americans of South Asian or Middle Eastern descent between September 11 and 17. Various crimes such as vandalism, arson, assault, shootings, harassment, and threats in numerous places were documented.[197][198]

Muslim American response

Muslim organizations in the United States were swift to condemn the attacks and called "upon Muslim Americans to come forward with their skills and resources to help alleviate the sufferings of the affected people and their families".[199] These organizations included the Islamic Society of North America, American Muslim Alliance, American Muslim Council, Council on American-Islamic Relations, Islamic Circle of North America, and the Shari'a Scholars Association of North America. Along with monetary donations, many Islamic organizations launched blood drives and provided medical assistance, food, and shelter for victims.[200][201][202]

International reactions

The attacks were denounced by mass media and governments worldwide. Across the globe, nations offered pro-American support and solidarity.[203] Leaders in most Middle Eastern countries, and Afghanistan, condemned the attacks. Iraq was a notable exception, with an immediate official statement that, "the American cowboys are reaping the fruit of their crimes against humanity".[204] While the government of Saudi Arabia officially condemned the attacks, privately many Saudis favored bin Laden's cause.[205][206] As in the United States, the aftermath of the attacks saw tensions increase in other countries between Muslims and non-Muslims.[207]

United Nations Security Council Resolution 1368 condemned the attacks, and expressed readiness to take all necessary steps to respond and combat all forms of terrorism in accordance with their Charter.[208] Numerous countries introduced anti-terrorism legislation and froze bank accounts they suspected of al-Qaeda ties.[209][210] Law enforcement and intelligence agencies in a number of countries arrested alleged terrorists.[211][212]

British Prime Minister Tony Blair said Britain stood "shoulder to shoulder" with the United States.[213] A few days later, Blair flew to Washington to affirm British solidarity with the United States. In a speech to Congress, nine days after the attacks, which Blair attended as a guest, President Bush declared "America has no truer friend than Great Britain."[214] Subsequently, Prime Minister Blair embarked on two months of diplomacy to rally international support for military action; he held 54 meetings with world leaders and travelled more than 40,000 miles (60,000 km).[215]

Vladimir Putin and his wife attending a commemoration service for the victims of the September 11 attacks on November 16, 2001

Tens of thousands of people attempted to flee Afghanistan following the attacks, fearing a response by the United States. Pakistan, already home to many Afghan refugees from previous conflicts, closed its border with Afghanistan on September 17, 2001. Approximately one month after the attacks, the United States led a broad coalition of international forces to overthrow the Taliban regime from Afghanistan for their harboring of al-Qaeda.[216] Though Pakistani authorities were initially reluctant to align themselves with the United States against the Taliban, they permitted the coalition access to their military bases, and arrested and handed over to the U.S. over 600 suspected al-Qaeda members.[217][218]

Military operations

At 2:40 p.m. in the afternoon of September 11, Secretary of DefenseDonald Rumsfeld was issuing rapid orders to his aides to look for evidence of Iraqi involvement. According to notes taken by senior policy official Stephen Cambone, Rumsfeld asked for, "Best info fast. Judge whether good enough hit S.H." (Saddam Hussein) "at same time. Not only UBL" (Osama bin Laden).[222] Cambone's notes quoted Rumsfeld as saying, "Need to move swiftly – Near term target needs – go massive – sweep it all up. Things related and not."[223][224] In a meeting at Camp David on September 15 the Bush administration rejected the idea of attacking Iraq in response to 9/11.[225]

The NATO council declared the attacks on the United States were an attack on all NATO nations which satisfied Article 5 of the NATO charter. This marked the first invocation of Article 5, which had been written during the Cold War with an attack by the Soviet Union in mind.[226]Australian Prime MinisterJohn Howard who was in Washington D.C. during the attacks invoked Article IV of the ANZUS treaty.[227] The Bush administration announced a War on Terror, with the stated goals of bringing bin Laden and al-Qaeda to justice and preventing the emergence of other terrorist networks.[228] These goals would be accomplished by imposing economic and military sanctions against states harboring terrorists, and increasing global surveillance and intelligence sharing.[229]

Effects

Health issues

Hundreds of thousands of tons of toxic debris containing more than 2,500 contaminants, including known carcinogens, were spread across Lower Manhattan due to the collapse of the Twin Towers.[235][236] Exposure to the toxins in the debris is alleged to have contributed to fatal or debilitating illnesses among people who were at ground zero.[237][238] The Bush administration ordered the Environmental Protection Agency (EPA) to issue reassuring statements regarding air quality in the aftermath of the attacks, citing national security, but the EPA did not determine that air quality had returned to pre-September 11 levels until June 2002.[239]

Health effects extended to residents, students, and office workers of Lower Manhattan and nearby Chinatown.[240] Several deaths have been linked to the toxic dust, and the victims' names were included in the World Trade Center memorial.[241] Approximately 18,000 people have been estimated to have developed illnesses as a result of the toxic dust.[242] There is also scientific speculation that exposure to various toxic products in the air may have negative effects on fetal development. A notable children's environmental health center is currently analyzing the children whose mothers were pregnant during the WTC collapse, and were living or working nearby.[243] A study of rescue workers released in April 2010 found that all those studied had impaired lung functions, and that 30–40% were reporting little or no improvement in persistent symptoms that started within the first year of the attack.[244]

Years after the attacks, legal disputes over the costs of illnesses related to the attacks were still in the court system. On October 17, 2006, a federal judge rejected New York City's refusal to pay for health costs for rescue workers, allowing for the possibility of numerous suits against the city.[245] Government officials have been faulted for urging the public to return to lower Manhattan in the weeks shortly after the attacks. Christine Todd Whitman, administrator of the EPA in the aftermath of the attacks, was heavily criticized by a U.S. District Judge for incorrectly saying that the area was environmentally safe.[246] Mayor Giuliani was criticized for urging financial industry personnel to return quickly to the greater Wall Street area.[247]

According to a new study, pregnant women living near the World Trade Center during the 9/11 terror attacks experienced higher-than-normal negative birth outcomes. The study by Princeton University's Woodrow Wilson School of Public and International Affairs found that these mothers were more likely to give birth prematurely and deliver babies with low birth weights. Their babies were also more likely to be admitted to neonatal intensive care units after birth (especially baby boys), according to the study led by the Wilson School's Janet Currie and Hannes Schwandt.[250]

Economic

As shown in this table, the 9/11 attacks had a major effect on the economy of New York City (in red), compared to the United States' economy overall (in blue).

The attacks had a significant economic impact on United States and world markets.[251] The stock exchanges did not open on September 11 and remained closed until September 17. Reopening, the Dow Jones Industrial Average (DJIA) fell 684 points, or 7.1%, to 8921, a record-setting one-day point decline.[252] By the end of the week, the DJIA had fallen 1,369.7 points (14.3%), at the time its largest one-week point drop in history.[253] In 2001 dollars, U.S. stocks lost $1.4 trillion in valuation for the week.[253]

In New York City, about 430,000 job-months and $2.8 billion dollars in wages were lost in the three months after the attacks. The economic effects were mainly on the economy's export sectors.[254] The city's GDP was estimated to have declined by $27.3 billion for the last three months of 2001 and all of 2002. The U.S. government provided $11.2 billion in immediate assistance to the Government of New York City in September 2001, and $10.5 billion in early 2002 for economic development and infrastructure needs.[255] Also hurt were small businesses in Lower Manhattan near the World Trade Center, 18,000 of which were destroyed or displaced, resulting in lost jobs and their consequent wages. Assistance was provided by Small Business Administration loans, federal government Community Development Block Grants, and Economic Injury Disaster Loans.[255] Some 31,900,000 square feet (2,960,000 m2) of Lower Manhattan office space was damaged or destroyed.[256] Many wondered whether these jobs would return, and if the damaged tax base would recover.[257] Studies of the economic effects of 9/11 show the Manhattan office real-estate market and office employment were less affected than first feared, because of the financial services industry's need for face-to-face interaction.[258][259]

North American air space was closed for several days after the attacks and air travel decreased upon its reopening, leading to a nearly 20% cutback in air travel capacity, and exacerbating financial problems in the struggling U.S. airline industry.[260]

Cultural

The impact of 9/11 extends beyond geopolitics into society and culture in general. Immediate responses to 9/11 included greater focus on home life and time spent with family, higher church attendance, and increased expressions of patriotism such as the flying of flags.[263] The radio industry responded by removing certain songs from playlists, and the attacks have subsequently been used as background, narrative or thematic elements in film, television, music and literature. Already-running television shows as well as programs developed after 9/11 have reflected post-9/11 cultural concerns.[264]9/11 conspiracy theories have become social phenomena, despite negligible support for such views from expert scientists, engineers, and historians.[265] 9/11 has also had a major impact on the religious faith of many individuals; for some it strengthened, to find consolation to cope with the loss of loved ones and overcome their grief; others started to question their faith or lost it entirely, because they couldn't reconcile it with their view of religion.[266][267]

The culture of America succeeding the attacks is noted for heightened security and an increased demand thereof, as well as paranoia and anxiety regarding future terrorist attacks that includes most of the nation. Psychologists have also confirmed that there has been an increased amount of national anxiety in commercial air travel.[268]

Investigations

FBI

Mohamed Atta, an Egyptian national, was the ringleader of the hijackers.

Immediately after the attacks, the Federal Bureau of Investigation started PENTTBOM, the largest criminal inquiry in the history of the United States. At its height, more than half of the FBI's agents worked on the investigation and followed a half-million leads.[276] The FBI concluded that there was "clear and irrefutable" evidence linking al-Qaeda and bin Laden to the attacks.[277]

The FBI was quickly able to identify the hijackers, including leader Mohamed Atta, when his luggage was discovered at Boston's Logan Airport. Atta had been forced to check two of his three bags due to space limitations on the 19-seat commuter flight he took to Boston.[278] Due to a new policy instituted to prevent flight delays, the luggage failed to make it aboard American Airlines Flight 11 as planned. The luggage contained the hijackers' names, assignments and al-Qaeda connections. "It had all these Arab-language (sic) papers that amounted to the Rosetta stone of the investigation", said one FBI agent.[279] Within hours of the attacks, the FBI released the names and in many cases the personal details of the suspected pilots and hijackers.[280][281] On September 27, 2001, they released photos of all 19 hijackers, along with information about possible nationalities and aliases.[282] Fifteen of the men were from Saudi Arabia, two from the United Arab Emirates, one from Egypt, and one from Lebanon.[283]

By midday, the U.S. National Security Agency and German intelligence agencies had intercepted communications pointing to Osama bin Laden.[284] Two of the hijackers were known to have travelled with a bin Laden associate to Malaysia in 2000[285] and hijacker Mohammed Atta had previously gone to Afghanistan.[286] He and others were part of a terrorist cell in Hamburg.[287] One of the members of the Hamburg cell was discovered to have been in communication with Khalid Sheik Mohammed who was identified as a member of al-Qaeda.[288]

Authorities in the United States and Britain also obtained electronic intercepts, including telephone conversations and electronic bank transfers, which indicate that Mohammed Atef, a bin Laden deputy, was a key figure in the planning of the 9/11 attacks. Intercepts were also obtained that revealed conversations that took place days before September 11 between bin Laden and an associate in Pakistan. In those conversations, the two referred to "an incident that would take place in America on, or around, September 11" and they discussed potential repercussions. In another conversation with an associate in Afghanistan, bin Laden discussed the "scale and effects of a forthcoming operation." These conversations did not specifically mention the World Trade Center or Pentagon, or other specifics.[289]

Origins of the 19 hijackers

Nationality

Number

Saudi Arabia

15

United Arab Emirates

2

Egypt

1

Lebanon

1

CIA

The Inspector General of the Central Intelligence Agency (CIA) conducted an internal review of the agency's pre-9/11 performance and was harshly critical of senior CIA officials for not doing everything possible to confront terrorism. He criticized their failure to stop two of the 9/11 hijackers, Nawaf al-Hazmi and Khalid al-Mihdhar, as they entered the United States and their failure to share information on the two men with the FBI.[290] In May 2007, senators from both major U.S. political parties drafted legislation to make the review public. One of the backers, Senator Ron Wyden said, "The American people have a right to know what the Central Intelligence Agency was doing in those critical months before 9/11."[291]

Congressional inquiry

In February 2002 the Senate Select Committee on Intelligence and the House Permanent Select Committee on Intelligence formed a joint inquiry into the performance of the U.S. Intelligence Community.[292] Their 832 page report released in December 2002[293] detailed failings of the FBI and CIA to use available information, including about terrorists the CIA knew were in the United States, in order to disrupt the plots.[294] The joint inquiry developed its information about possible involvement of Saudi Arabian government officials from non-classified sources.[295] Nevertheless, the Bush administration demanded 28 related pages remain classified.[294] In December 2002 the inquiry's chair Bob Graham (D-FL) revealed in an interview that there was "evidence that there were foreign governments involved in facilitating the activities of at least some of the terrorists in the United States."[296] September 11th victim families were frustrated by the unanswered questions and redacted material from the Congressional inquiry and demanded an independent commission.[294] September 11th victim families,[297] members of congress[298][299] and the Saudi Arabian government are still seeking release of the documents.[300][301]

9/11 Commission

The National Commission on Terrorist Attacks Upon the United States (9/11 Commission), chaired by Thomas Kean and Lee H. Hamilton, was formed in late 2002 to prepare a thorough account of the circumstances surrounding the attacks, including preparedness for and the immediate response to the attacks.[302] On July 22, 2004, the Commission issued the 9/11 Commission Report. The report detailed the events of 9/11, found the attacks were carried out by members of al-Qaeda, and examined how security and intelligence agencies were inadequately coordinated to prevent the attacks. Formed from an independent bipartisan group of mostly former Senators, Representatives, and Governors, the commissioners explained, "We believe the 9/11 attacks revealed four kinds of failures: in imagination, policy, capabilities, and management".[303] The Commission made numerous recommendations on how to prevent future attacks, and in 2011 was dismayed that several of its recommendations had yet to be implemented.[304]

Collapse of the World Trade Center

The exterior support columns from the lower level of the south tower remained standing after the building collapsed.

The U.S. National Institute of Standards and Technology (NIST) investigated the collapses of the Twin Towers and 7 WTC. The investigations examined why the buildings collapsed and what fire protection measures were in place, and evaluated how fire protection systems might be improved in future construction.[305] The investigation into the collapse of 1 WTC and 2 WTC was concluded in October 2005 and that of 7 WTC was completed in August 2008.[306]

NIST found that the fireproofing on the Twin Towers' steel infrastructures was blown off by the initial impact of the planes and that, had this not occurred, the towers likely would have remained standing.[307] A 2007 study of the north tower's collapse published by researchers of Purdue University determined that, since the plane's impact had stripped off much of the structure's thermal insulation, the heat from a typical office fire would have softened and weakened the exposed girders and columns enough to initiate the collapse regardless of the number of columns cut or damaged by the impact.[308][309]

The director of the original investigation stated that, "the towers really did amazingly well. The terrorist aircraft didn’t bring the buildings down; it was the fire which followed. It was proven that you could take out two thirds of the columns in a tower and the building would still stand."[310] The fires weakened the trusses supporting the floors, making the floors sag. The sagging floors pulled on the exterior steel columns causing the exterior columns to bow inward. With the damage to the core columns, the buckling exterior columns could no longer support the buildings, causing them to collapse. Additionally, the report found the towers' stairwells were not adequately reinforced to provide adequate emergency escape for people above the impact zones.[311] NIST concluded that uncontrolled fires in 7 WTC caused floor beams and girders to heat and subsequently "caused a critical support column to fail, initiating a fire-induced progressive collapse that brought the building down".[306]

Rebuilding

On the day of the attacks, New York City mayor Rudy Giuliani stated: "We will rebuild. We're going to come out of this stronger than before, politically stronger, economically stronger. The skyline will be made whole again."[312]

The damaged section of the Pentagon was rebuilt and occupied within a year of the attacks.[313] The temporary World Trade Center PATH station opened in late 2003 and construction of the new 7 World Trade Center was completed in 2006. Work on rebuilding the main World Trade Center site was delayed until late 2006 when leaseholder Larry Silverstein and the Port Authority of New York and New Jersey agreed on financing.[314] The construction of One World Trade Center began on April 27, 2006, and reached its full height on May 20, 2013. The spire was installed atop the building at that date, putting 1 WTC's height at 1,776 feet (541 m) and thus claiming the title of the tallest building in the Western Hemisphere.[315] 1 WTC finished construction and opened on November 3, 2014.[316]

On the World Trade Center site, three more office towers are expected to be built one block east of where the original towers stood. Construction has begun on all three of these towers.[317]

Memorials

The Tribute in Light on September 11, 2014, on the thirteenth anniversary of the attacks, seen from Bayonne, New Jersey. The tallest building in the picture is the new One World Trade Center.

In the days immediately following the attacks, many memorials and vigils were held around the world, and photographs of the dead and missing were posted around Ground Zero. A witness described being unable to "get away from faces of innocent victims who were killed. Their pictures are everywhere, on phone booths, street lights, walls of subway stations. Everything reminded me of a huge funeral, people quiet and sad, but also very nice. Before, New York gave me a cold feeling; now people were reaching out to help each other.”[318]

One of the first memorials was the Tribute in Light, an installation of 88 searchlights at the footprints of the World Trade Center towers.[319] In New York, the World Trade Center Site Memorial Competition was held to design an appropriate memorial on the site.[320] The winning design, Reflecting Absence, was selected in August 2006, and consists of a pair of reflecting pools in the footprints of the towers, surrounded by a list of the victims' names in an underground memorial space.[321]

The Pentagon Memorial was completed and opened to the public on the seventh anniversary of the attacks in 2008.[322][323] It consists of a landscaped park with 184 benches facing the Pentagon.[324] When the Pentagon was repaired in 2001–2002, a private chapel and indoor memorial were included, located at the spot where Flight 77 crashed into the building.[325]

In Shanksville, a permanent Flight 93 National Memorial is planned to include a sculpted grove of trees forming a circle around the crash site, bisected by the plane's path, while wind chimes will bear the names of the victims.[326] A temporary memorial is located 500 yards (457 m) from the crash site.[327] New York City firefighters donated a cross made of steel from the World Trade Center and mounted on top of a platform shaped like the Pentagon.[328] It was installed outside the firehouse on August 25, 2008.[329] Many other permanent memorials are elsewhere. Scholarships and charities have been established by the victims' families, and by many other organizations and private figures.[330]

On every anniversary, in New York City, the names of the victims who died there are read out against a background of somber music. The President of the United States attends a memorial service at the Pentagon,[331] and asks Americans to observe Patriot Day with a moment of silence. Smaller services are held in Shanksville, Pennsylvania, which are usually attended by the President's spouse.

Notes

^9/11 is pronounced "nine eleven". The slash is not part of the pronunciation. The name is frequently used in British English as well as in American English, although the dating conventions differ.

References

Citations

^ abc"Bin Laden claims responsibility for 9/11". CBC News. October 29, 2004. Retrieved 2011-09-01. Al-Qaeda leader Osama bin Laden appeared in a new message aired on an Arabic TV station Friday night, for the first time claiming direct responsibility for the 2001 attacks against the United States.

^"Bin Laden on tape: Attacks 'benefited Islam greatly'". CNN. December 14, 2001. Archived from the original on 2007-12-27. Retrieved 2013-11-24. Reveling in the details of the fatal attacks, bin Laden brags in Arabic that he knew about them beforehand and says the destruction went beyond his hopes. He says the attacks "benefited Islam greatly".

^"'We left out nuclear targets, for now'". The Guardian (London). March 4, 2003. Archived from the original on 2008-03-02. Retrieved 2011-09-03. Yosri Fouda of the Arabic television channel al-Jazeera is the only journalist to have interviewed Khalid Sheikh Mohammed, the al-Qaeda military commander arrested at the weekend. Here he describes the two-day encounter with him and his fellow organiser of September 11, Ramzi bin al- Shibh: […] Summoning every thread of experience and courage, I looked Khalid in the eye and asked: 'Did you do it?' The reference to September 11 was implicit. Khalid responded with little fanfare: 'I am the head of the al-Qaeda military committee,' he began, 'and Ramzi is the coordinator of the Holy Tuesday operation. And yes, we did it.'

^bin Laden, Osama. "Full transcript of bin Ladin's speech". Al Jazeera. Retrieved 2012-04-10. So I shall talk to you about the story behind those events and shall tell you truthfully about the moments in which the decision was taken, for you to consider

^See also the 1998 Al-Qaeda fatwā: "The ruling to kill the Americans and their allies – civilians and military – is an individual duty for every Muslim who can do it in any country in which it is possible to do it, in order to liberate the al-Aqsa Mosque and the holy mosque [Mecca] from their grip, and in order for their armies to move out of all the lands of Islam, defeated and unable to threaten any Muslim." Quoted from "Al Qaeda's Second Fatwa". PBS NewsHour. Public Broadcasting Service. Archived from the original on 2013-11-28. Retrieved 2014-05-29.

^Bernard Lewis, 2004. In Bernard Lewis's 2004 book The Crisis of Islam: Holy War and Unholy Terror, he argues that animosity toward the West is best understood with the decline of the once powerful Ottoman empire, compounded by the import of western ideas — Arab socialism, Arab liberalism and Arab secularism. During the past three centuries, according to this interpretation, the Islamic world has lost its dominance and its position of leadership in the world, and has fallen behind both the modern West and the rapidly modernizing Orient. The resulting widening gap poses increasingly severe problems, both practical and emotional, for which the rulers, thinkers, and rebels of Islam have not yet found effective answers.

^In an essay titled "The spirit of terrorism", Jean Baudrillard described 9/11 as the first global event that "questions the very process of globalization". Baudrillard. "The spirit of terrorism". Retrieved 2011-06-26.

^In an essay entitled "Somebody Else's Civil War", Michael Scott Doran argues the attacks are best understood as part of a religious conflict within the Muslim world and that Bin Laden's followers "consider themselves an island of true believers surrounded by a sea of iniquity". Hoping that U.S. retaliation would unite the faithful against the West, bin Laden sought to spark revolutions in Arab nations and elsewhere. Doran argues the Osama bin Laden videos attempt to provoke a visceral reaction in the Middle East and ensure that Muslim citizens would react as violently as possible to an increase in U.S. involvement in their region. ("Somebody Else's Civil War". Foreign Affairs. Retrieved 2009-12-05. Reprinted in Hoge, James F.; Rose, Gideon (2005). Understanding the War on Terror. New York: Norton. pp. 72–75. ISBN978-0-87609-347-4.)

^In The Osama bin Laden I Know, Peter Bergen argues the attacks were part of a plan to cause the United States to increase its military and cultural presence in the Middle East, thereby forcing Muslims to confront the idea of a non-Muslim government and to eventually establish conservative Islamic governments in the region.(Bergen (2006), p. 229.)

^Schechter DS, Coates SW, First E (2002). Observations of acute reactions of young children and their families to the World Trade Center attacks. Journal of ZERO-TO-THREE: National Center for Infants, Toddlers, and Families, 22(3), 9–13.

^"Security Council Condemns, 'In Strongest Terms', Terrorist Attacks on the United States". United Nations. September 12, 2001. Retrieved 2006-09-11. The Security Council today, following what it called yesterday’s "horrifying terrorist attacks" in New York, Washington, D.C., and Pennsylvania, unequivocally condemned those acts, and expressed its deepest sympathy and condolences to the victims and their families and to the people and Government of the United States.

^"Statement by the North Atlantic Council". NATO. September 15, 2001. Retrieved 2011-09-04. Article 5: The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area. Any such armed attack and all measures taken as a result thereof shall immediately be reported to the Security Council. Such measures shall be terminated when the Security Council has taken the measures necessary to restore and maintain international peace and security.

^Irfanoglu, A.; Hoffmann, C. M. (2008). "Engineering Perspective of the Collapse of WTC-I". Journal of Performance of Constructed Facilities (American Society of Civil Engineers) 22: 62. doi:10.1061/(ASCE)0887-3828(2008)22:1(62). As the aircraft debris went through several stories in the tower, much of the thermal insulation on the core columns would have been scoured off. Under such conditions, the ensuing fire would be sufficient to cause instability and initiate collapse. From an engineering perspective, impact damage to the core structure had a negligible effect on the critical thermal load required to initiate collapse in the core structure.

^Tally, Steve (June 12, 2007). "Purdue creates scientifically based animation of 9/11 attack". Purdue News Service. Retrieved 2011-09-04. The aircraft moved through the building as if it were a hot and fast lava flow," Sozen says. "Consequently, much of the fireproofing insulation was ripped off the structure. Even if all of the columns and girders had survived the impact – an unlikely event – the structure would fail as the result of a buckling of the columns. The heat from an ordinary office fire would suffice to soften and weaken the unprotected steel. Evaluation of the effects of the fire on the core column structure, with the insulation removed by the impact, showed that collapse would follow whatever the number of columns cut at the time of the impact.